System and method for removal of recalcitrant organic compounds from water

ABSTRACT

The present inventions are directed to systems and methods to increase the removal of PFAS and other recalcitrant organic compound contaminants from water, and particularly ground and drinking water, using sub-micron powdered activated carbon.

FIELD OF THE INVENTION

The present inventions relate to systems and methods for removingrecalcitrant organic compounds, including per and poly fluoroalkylsubstances, from water. In particular, the present inventions relate tosystems and methods for removing such contaminants from water usingsub-micron powdered activated carbon in conjunction with ceramicmembrane filtration. The present inventions also relate to systems andmethods for the concentration and removal of the exhausted carbon.

BACKGROUND OF THE INVENTION

Per and poly fluoroalkyl substances (“PFAS”), including their precursorsand related ranges, such as perfluorooctane sulfuric acid (“PFOS”) andperfluorooctanic acid (“PFOA”), are compounds resistant to water andoil. They are man-made compounds that have been used in a wide varietyof industries, including carpeting, upholstery and fire fighting foams.However, such compounds are bioaccumulative and known carcinogens andtheir removal from water, and particularly from ground water anddrinking water, is an important environmental concern. Due to the strongfluorine-carbon bond, PFAS compounds are resistant to common treatmentmethods including biological and chemical oxidation.

One of the more common approaches to the removal of PFAS from water isgranular activated carbon (“GAC”) or powdered activated carbon (“PAC”)treatment systems. As its name suggests, GAC uses granulated activatedcarbon to remove various contaminants, including organic recalcitrantcompounds such as PFAS and others. In a typical GAC system, a tankcontains the granulated activated carbon, the tank being of a sufficientsize to retain the flow of water to be treated a sufficient time for thecontaminants to react with the GAC. During the reaction, the PFAS andother organic compounds adhere to the surface of the granulatedactivated carbon, i.e., they are adsorbed by the granulated activatedcarbon.

After use, the adsorption of the organic contaminant compounds isreduced to such a point that the system is no longer effective. In otherwords, when the adsorption of contaminants is less than the desiredtreatment requirements, breakthrough is said to occur. At that point,the typical system must be shut down and the granulated activated carbonremoved and properly remediated. Depending upon the contaminantsfiltered, the spent GAC, particularly with the adsorbed PFAS, must behauled away and incinerated. In addition, because of the rapidbreakthrough of GAC systems, and the need for frequent GAC regenerationand treatment, the operating costs for GAC treatment are relativelyhigh. A relatively large plant footprint is also required for GACtreatment systems.

The ability of the GAC to adsorb contaminants, and the typicalbreakthrough time, is related to the mean particle diameter (“MPD”) ofthe carbon. In conventional GAC systems, the MPD is approximately 1,600microns. Even in systems using PAC, the MPD of the PAC is 45 microns orhigher. In both GAC and PAC, PFAS adsorption is aided by the carbon'sporous structure which includes macro-pores, micro-pores and meso-pores.The primary adsorption mechanism depends on the size of the contaminant,with macropores and mesopores having been found to be most important forPFAS removal. With the larger MPD for both GAC and PAC, access to theinterior pores is limited and can result in breakthrough despite theavailable surface area for adsorption deep within the carbon particle.As indicated, breakthrough times are decreased with the larger MPD andcarbon removal and disposal costs are increased. In addition, typicalGAC systems do not effectively remove short chain length (i.e., 4, 6 and7 carbon chained) PFAS compounds.

Thus, there is a need to increase the removal of PFAS and otherrecalcitrant organic compound contaminants from water, and particularlyground and drinking water. There is also a need to increase thebreakthrough time of typical GAC filtration systems and to decrease theburden and expense of used material disposal. In the present inventions,it has been determined that use of sub-micron powdered activated carbon(“SPAC”) and its smaller particle size provides higher surface area andincreased quantity of mesopores, resulting in a lower usage rate andfaster adsorption, requiring smaller volumes. SPAC is also moreeffective at removing short chain PFAS, for which known treatments areineffective. The greater surface area and improved access to mesoporesand macropores provided with SPAC and the present inventions has shownto increase PFAS adsorption by more than 500 times that of GAC basedupon a given amount of carbon. In addition, the present inventionsprovide for the thickening or concentration of spent SPAC to reduce thedisposal costs.

SUMMARY OF THE INVENTION

Accordingly, the present inventions preserve the advantages of knownPFAS removal systems and methods and also provide new features andadvantages.

An object of the present invention is to use sub-micron powderedactivated carbon (“SPAC”) to remove recalcitrant organic compoundcontaminants from water, the contaminants including PFAS, 1, 4-dioxane,BTEX and many others.

Another object of the present invention is to provide a sorptionreactor, and preferably a pressurized sorption reactor, to provide adetention time for the SPAC and water slurry sufficient for the SPAC toadsorb the contaminants from the influent of water to be treated.

An additional object of the present invention is to use a ceramicmembrane filter, and preferably a high velocity cross-flow ceramicmembrane filter, to separate the filtered water from the SPAC withadsorbed contaminants and to return a portion of the bulk liquid to thesorption reactor.

A further object of the present invention is to increase SPAC recoveryand concentration to reduce the removal and disposal of used SPAC.

Still an additional object of the present invention is to maintain theSPAC in a closed loop system as treated water is separated from the SPACusing high strength, high velocity cross-flow ceramic membrane filtersand a bleed and feed SPAC conservation and recovery system.

Still another object of the present invention is to scour and clean themembranes of the ceramic membrane filtration system while filtering thetreated water from the SPAC and its adsorbed contaminants.

Still a further object of the present invention is to use a ceramicmembrane filter to retain SPAC in the system so that it may continue toremove soluble and recalcitrant organic compounds, including PFAS.

Yet another object of the present invention is to use a high velocitycross-flow ceramic membrane filter to reduce backwash frequency andbackwash waste.

Yet a further object of the present invention is to maximize contaminantadsorption and to reduce SPAC usage and disposal.

Still yet another object of the present invention is to concentratespent SPAC to reduce the frequency and amount of removal and/ordisposal.

In accordance with the objects of the present invention, a method forremoving contaminants from water is provided. The steps include: addingsub-micron powdered activated carbon (SPAC) to an influent flow of waterto be treated; combining the SPAC with the water to be treated;introducing a SPAC and water mixture or slurry into a sorption reactorfor treatment; permitting the mixture to remain in the sorption reactorfor a sufficient detention time for the SPAC to adsorb contaminants inthe water; and transferring the mixture or slurry from the sorptionreactor using a recycle pump to a high velocity ceramic membrane filterunit operating in cross-flow filtration wherein the treated water isdischarged as permeate and the SPAC slurry is returned to the sorptionreactor as retentate. The method may also include removing the SPAC andadsorbed contaminant concentrate from the ceramic membrane filter via aconcentrate line upon the SPAC reaching breakthrough; and adding newSPAC to the influent flow of water to continue contaminant removal.Further, in the preferred method, the SPAC and adsorbed contaminants arethickened for removal by terminating the influent flow to the sorptionreactor and continuing operation of the recycle pump until the retentateis thickened and is thereafter removed via the concentrate line fordisposal. The membranes of the ceramic membrane filter have a nominalpore size barrier of approximately 0.1 microns. In a preferred method,the influent flow is 1 Qi and the mixture of SPAC and influent is pumpedat 10 times the influent (10 Qi) from the sorption reactor to theceramic membrane filter. Also as preferred, the permeate is dischargedat a rate of 1 times the influent flow (1 Qi) from the ceramic membranefilter and the retentate is returned to the sorption reactor at a rateof Qr, which is preferably 9 times the influent flow (9 Qi). Preferably,the SPAC has a mean particle diameter below approximately 1 micron.

Also provided is a system for removing contaminants, including PFAS,from water. The system includes: a pressurized sorption reactor in fluidcommunication with an influent line, and a SPAC feed line incommunication with the influent line to add SPAC to the influent, thesorption reactor receiving an influent flow of water to be treated andsub-micron powdered activated carbon (SPAC), the sorption reactorcapable of retaining the influent and SPAC slurry a sufficient retentiontime so that the contaminants to be removed are adsorbed by the SPAC inthe slurry; a slurry effluent line in communication with a discharge ofthe sorption reactor and a recycle pump in the slurry effluent line; across-flow ceramic membrane filter in fluid communication with theslurry effluent line of the sorption reactor, the recycle pumptransferring the SPAC with adsorbed contaminants at a high flow rate tothe ceramic membrane filter unit which separates treated water from thecontaminant-adsorbed SPAC as permeate; a permeate line in fluidcommunication with the ceramic membrane filter for removing the treatedwater as permeate; a retentate line in fluid communication with theceramic membrane filter and the sorption reactor to return the SPACslurry to the influent line; and a concentrate line for removing SPACupon breakthrough. The preferred system uses SPAC that has a meanparticle diameter below approximately 1 micron on wherein the ceramicmembrane filter has a nominal pore size barrier of approximately 0.1micron.

An embodiment of the system may also include a SPAC feed system in fluidcommunication with the influent line.

Inventor's Definition of the Terms

The following terms which may be used in the various claims and/orspecification of this patent are intended to have their broadest meaningconsistent with the requirements of law:

“Influent” or “influent flow” (also referred to as Qi) as used hereinrefers to the liquid (water or wastewater) to be treated that isintroduced into the contaminant removal system.

“Permeate” or “filtrate” as used herein shall refer to the treated fluidor fluid flow after treatment with the contaminant removal system andseparation of the SPAC and its adsorbed contaminants.

“Retentate” or “retentate flow (Qr)” as used herein refers to the SPACcontaining bulk liquid or slurry from which the permeate or filtrate hasbeen removed.

“SPAC” as used herein refers to sub-micron, or super-fine powderedactivated carbon, preferably wood based, and preferably with a meanparticle diameter below approximately 1 micron.

“PFAS” as used herein refer to a broad range of per or poly fluoroalkylsubstances, including perflourooctane sulfonic acid (PFOS) andperflourooctanoic acid (PFOA), as well as short chain perflouroalkylacids (PFAA) and its precursers. PFAS as used herein may also refergenerally to other recalcitrant organic compounds.

“Breakthrough” as used herein refers to the SPAC that is no longercapable of adsorbing sufficient levels of contaminants for desired andeffective treatment.

Where alternative meanings are possible, in either the specification orclaims, the broadest meaning is intended consistent with theunderstanding of those of ordinary skill in the art. All words used inthe claims are intended to be used in the normal, customary usage ofgrammar, the trade and the English language.

BRIEF DESCRIPTION OF THE DRAWINGS

The stated and unstated objects, features and advantages of the presentinventions (sometimes used in the singular, but not excluding theplural) will become apparent from the following descriptions anddrawings, wherein like reference numerals represent like elements in thevarious views, and in which:

FIG. 1 is a schematic view of the preferred contaminant removal systemof the present invention in its basic form.

FIG. 2 is a schematic view of a more comprehensive preferred contaminantremoval system of the present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Set forth below is a description of what is currently believed to be thepreferred embodiments or best representative examples of the inventionsclaimed. Future and present alternatives and modifications to theembodiments and preferred embodiments are contemplated. Any alternativesor modifications which make insubstantial changes in function, purpose,structure or result are intended to be covered by the claims of thispatent.

The preferred PFAS removal system and method of the present inventionsis shown in its basic form in FIG. 1. The system includes an influentline 11 that introduces the flow (Qi) of influent of water to be treatedinto the system. SPAC 12 is added to the influent (Qi) via a SPAC feedline 13, typically using a carbon feed assembly or other means ashereinafter described. A mixer 14 may optionally be included to help mixthe influent water and the SPAC 12 forming the bulk liquid or slurry tobe treated. The SPAC 12 and influent slurry is then pumped by a feedpump 16 through slurry feed line 15 to a sorption reactor 20. Feed pump16 is sized to pump the influent flow and SPAC slurry at a designed flowrate (Qi). Feed pump 16 pumps the influent at Qi with the SPAC slurry tosorption reactor 20 via slurry feed line 15.

In a preferred embodiment, the systems and method utilize a wood basedSPAC 12 having a mean particle diameter (MPD) below approximately 1micron. The use of the sub-micron powdered particles provides a higherexterior surface area per unit mass and increased quantity of and accessto mesospores contained in the particles to permit faster, moreeffective contaminant adsorption. It also permits greater contaminantexposure and a lower ratio of usage. As a result, it has proveneffective in, among other things, short chain PFAS removal.

SPAC 12 is not believed to be currently a stocked, readily availablematerial because of its relatively low current demand. However, it maybe readily manufactured from GAC and/or PAC, of which there are manyknown manufacturers as will be understood by those of skill in the art.Some known GAC/PAC manufacturers include Asbury Carbons, Inc., NalcoWater and Calgon Carbon. These and other GAC/PAC manufacturers also havegrinding processes available to produce SPAC. For example, Asbury Carbonhas a readily available grinding process that can product SPAC from GACor PAC with very little lead time. Thus, the sources of SPAC of thepresent inventions are readily available to those of skill in the art.

In a preferred embodiment, the SPAC 12 will be manufactured and shippedto the treatment site in a liquid slurry for ease of handling andultimate use. For example, a 10% slurry of 1 micron SPAC and water (100grams of Carbon/liter) has been found to be desirable for use in thepresent inventions. As hereinafter described, the original SPAC 12slurry is further diluted by the influent water to be treated to theworking concentration to be transferred to the sorption reactor 20. In apreferred embodiment where the SPAC slurry is 100 grams of carbon/liter,the slurry is diluted to approximately 0.5 to 2 grams of carbon/liter inthe sorption reactor 20. These concentrations are merely illustrativeand not limitations.

Sorption reactor 20 is the vessel in which, among other things, thewater to be treated is in contact with the SPAC 12 or SPAC slurry asufficient time so that the PFAS may be adsorbed by the SPAC 12. Thesorption tank 20 serves as a reaction chamber for the SPAC 12 and waterto be treated such that the PFAS and other contaminants are adsorbed bythe SPAC 12 in the sorption tank 20. The sorption reactor 20 provides adesired and/or designed detention time of the SPAC/influent slurry suchthat the PFAS and other contaminants may be sufficiently adsorbed by theSPAC 12.

In a preferred embodiment, the sorption reactor 20 is sized toaccommodate at least ten times the influent flow (10 Qi) as hereinafterdescribed. It will be understood by those of skill in the art thatsorption reactor 20 is also sized to provide a desired detention time toaid the SPAC's adsorption of PFAS and other contaminants. The larger thesorption reactor 20 at a given flow, the longer the detention time it iscapable of providing. In a preferred embodiment, a detention time ofbetween 30-60 minutes at the influent flow (Qi) has been determined tobe satisfactory for the reaction between the SPAC and the PFAS in theinfluent having an exemplary influent from (Qi) of 100 gallons/minute.Other detention times will also suffice depending upon the desiredtreatment parameters and influent flows. Thus, in a system where Qi is100 gallons/minute and a detention time in sorption reactor 20 is onehour, sorption reactor 20 must accommodate at least 6,000 gallons.

A preferred sorption reactor 20 of the present invention is apressurized tank that is closed to the atmosphere. To preventshort-circuiting, baffles 21 (see FIG. 2) may be included in thesorption reactor 20. It will be understood by those of skill in the artthat non-pressurized tanks may be utilized. However, such tanks wouldhave to be relatively tall and/or would require a substantially largerenergy requirement.

The SPAC adsorbs the PFAS and other contaminants in sorption reactor 20.After sufficient detention time in the sorption reactor 20, the SPAC andbulk liquid reacted slurry is then pumped via slurry effluent line 22 toa ceramic membrane filter unit 30 using a recycle pump 26. In thepreferred embodiment, the recycle pump 26 is sized to pump ten times theinfluent flow (10 Qi) through slurry effluent line 22 to ceramicmembrane filter 30.

The ceramic membrane filter unit 30 provides important unique functionsof the present inventions. First, the ceramic membrane filter 30separates the SPAC and adsorbed contaminants from the treated liquid tobe removed as clean permeate via permeate line 32. The ceramic membranefilter also returns SPAC slurry to the sorption reactor 20 for furthertreatment of influent which reduces SPAC consumption. Third, the ceramicmembrane filter 30 also serves to concentrate and thicken the SPAC 12upon breakthrough or exhaustion that aids in SPAC 12 disposal, withoutthe need for complicated additional equipment.

In a preferred embodiment, the ceramic membrane filter 30 has a 0.1micron nominal pore size barrier. The small pore size results in highpermeability and reduced pressure loss across each membrane of theceramic membrane filter 30. As will be understood by those of skill inthe art, suitable ceramic membrane filters 30 are available from anumber of vendors, including Aqua-Aerobic Systems, Inc. (seewww.aqua-aerobic.com).

In the preferred embodiment, the ceramic membrane filter 30 is operatedin cross-flow filtration mode. As preferred, recycle pump 26 sends theSPAC/liquid slurry to the ceramic membrane filter 30 via slurry effluentline 22 at 10 times the influent flow rate or 10 Qi. The membranes ofthe ceramic membrane filter 30 separate the treated liquid from the SPACand liquid slurry. The treated water is discharged as permeate viapermeate line 32, preferably at the approximate rate of the initialinfluent rate of flow Qi. The SPAC and bulk liquid not discharged aspermeate is discharged from ceramic membrane filter 30 as retentate (Qr)via retentate line 36, preferably at the rate of 9 times the initialflow or 9 Qi. The retentate is returned upstream of the sorption reactor20, either to slurry feed line 15 or directly to sorption reactor 20.Among other things, the return of the SPAC laden retentate slurryincreases the concentration of SPAC 12 in the sorption reactor 20,thereby requiring less virgin SPAC 12 to be added to the system. Thisalso facilitates enhanced PFAS adsorption by the SPAC 12. Ceramicmembrane filter 30 is also provided with a concentrate exit 37 in fluidcommunication with concentrate removal line 38 to remove spent SPAC 12after breakthrough.

Importantly, pumping high velocity slurry at 10 Qi to the ceramicmembrane filter 30, while only removing 1 Qi as permeate, scours themembranes 31 inside the ceramic membrane filter 30. This results inmaintaining clean membranes 31 and a high permeability of the membranes31. It also reduces the frequency of backwashing requirements. The highvelocity through the ceramic membrane filter 30 further reduces theopportunity for bio-growth, which helps maintain filtering efficiencyand reduces the need for frequent backwashing or chemical conditioning.In the preferred embodiment, where 10 Q is pumped 26 to the ceramicmembrane filter 30, 1 Qi is removed as permeate via permeate line 32. Asa result, 9 Q (9 Qr) is returned to the sorption reactor 20 as retentatevia retentate line 36. It will be understood by those of skill in theart that these flows are exemplary and/or preferred and that other ratesmay be used consistent with the present inventions.

The foregoing describes the basic system and method for PFAS removalusing SPAC, the sorption reactor 20 and a ceramic membrane filter 30 ofthe present inventions. In addition, a more comprehensive system of thepresent inventions is described herein by reference to FIG. 2. Thesystem and method of SPAC thickening and removal is also described byreference to FIG. 2, although thickening and removal is also part of thebasic system shown in FIG. 1.

As shown in FIG. 2, a SPAC feed system 40 is provided as a substitutefor the direct feed of SPAC 12 to influent line 11 and the use ofoptional mixer 14. The SPAC feed system 40 includes a tank 41 and amixer 42 that mixes the SPAC slurry for use in the system. Specifically,in the preferred embodiment, a 10% SPAC slurry (e.g., 100 grams ofcarbon/liter) is added to tank 41 and mixed by mixer 42. The SPAC slurryis pumped from tank 41 using SPAC feed pump 43 through SPAC feed line 13to influent line 11. The mixture or slurry, via slurry feed line 15, isthen pumped using feed pump 16 to the sorption reactor 20, preferably ata rate of Qi. In a preferred embodiment, the 10% SPAC concentration isdiluted to approximately 0.5-2 grams of carbon/liter in the sorptionreactor 20. As shown schematically, a preferred sorption reactor 20includes one or more baffles 21 to help prevent short-circuiting. Uponsufficient detention time for the SPAC 12 to adsorb the contaminants,the bulk liquid is pumped to ceramic membrane filter 30 via slurryeffluent line 22 and recycle pump 26. Again, the preferred pumping is at10 Qi into the ceramic membrane filter 30 and recycle pump 26 sizedaccordingly.

As with the embodiment of FIG. 1, the ceramic membrane filter 30separates the permeate from the SPAC 12 and its adsorbed contaminants.The permeate is removed from the ceramic membrane filter 30 at a rate of1 Qi via permeate line 32. In this embodiment, however, a permeate tank50 is provided that is in fluid communication with permeate line 32.Permeate from ceramic membrane filter 30 is transferred to the permeatetank 50 and may be removed via permeate drain 52 as treated effluent orstored for use in backwashing as hereinafter described.

In the embodiment of FIG. 2, a backwash line 62 is in fluidcommunication with permeate tank 50 for removal of permeate for use inbackwashing. A backwash pump 61 is also provided in backwash line 62.Backwash line 62 is in fluid communication with a backwash tank 70.

Backwash tank 70 is then in fluid communication with permeate line 32 ofthe ceramic filter membrane unit 30. When backwashing is desired orrequired, permeate is pumped from permeate tank 50 by backwash pump 61to backwash tank 70. The permeate from backwash tank 70 flows frombackwash line 62 to permeate line 32 which communications with theceramic membrane filter 30. This reverses flow through the ceramicmembrane filter 30 to backwash the membranes 31 as hereinafterdescribed.

An optional chemical feed tank 60 may also be provided. Chemical feedtank 60 is in fluid communication with chemical feed line 65, whichincludes a chemical feed pump 64. Chemical feed line 65 is in turn incommunication with backwash line 62. Chemical feed tank 60 contains asolution of chemicals that may be used when backwashing the membranes ofceramic membrane filter 30. Such chemicals may include NaOCl and citricacid to aid in cleaning the membranes. Other chemicals may be used asunderstood by those of skill in the art. Thus, when chemicals aredesired for use in backwashing, the chemical solution is pumped bychemical feed pump 64, through chemical feed line 65 and into thepermeate flow of backwash line 62.

In addition, an optional air supply 80 may be provided. Air supply 80 isin fluid communication with an air supply line 81. Air supply line 81 isin fluid communication with backwash tank 70 and retentate line 36. Airsupply 80 may be provided in certain systems for use in backwashing.When backwashing is desired, air supply 80 pressurizes backwash tank 70through air supply line 81 until a pressure setting is reached and thenair valve 83 closes. Then backwash valve 63 is opened and releases thepressurized permeate from the backwash tank 70 through membrane filter30 to help clean the membranes 31.

An important aspect of the present inventions is the thickening,dewatering and removal of the spent SPAC 12. A preferred system andmethod will be described by reference to FIG. 2. For PFAS and otherorganic contaminant removal, a flow of influent at a rate of Qi isintroduced at influent line 11 (e.g., 100 gallons/minute). Using SPACfeed pump 43, the SPAC solution (e.g., 100 grams of carbon/liter) ispumped from SPAC tank 41 through an open SPAC feed valve 18 via SPACfeed line 13. The influent and SPAC slurry is pumped by feed pump 16 tosorption tank 20 via slurry feed line 15. The slurry is pumped intosorption reactor 20 at a rate of Qi. The SPAC 12 and influent slurry aredetained in sorption reactor 20 for the desired retention time, wherebythe PFAS and other contaminants are adsorbed into the SPAC 12. Theconcentration of SPAC 12 slurry in the sorption reactor 20 may be anexemplary 0.5-2 grams of carbon/liter.

The SPAC with adsorbed contaminants and bulk liquid slurry istransferred from sorption reactor 20 to the ceramic membrane filter 30for filtration. Specifically, the slurry is pumped using recycle pump 26along slurry effluent line 22, through open recycle valve 27 into theceramic membrane filter 30. As previously discussed, recycle pump 26 issized to pump 10 times the influent flow (10 Qi) into the ceramicmembrane filter 30. The membranes of the ceramic membrane filter 30separate the permeate from the SPAC/influent slurry.

The permeate is discharged from ceramic membrane filter 30 via permeateline 32 through open permeate valve 33 and into permeate tank 50 whereit may be removed via permeate removal line 52. The retentate is removedfrom ceramic membrane filter 30 through retentate line 36 and openretentate valve 34 to be returned to sorption reactor 20. The retentateis returned to the sorption reactor 20 at a flow rate of Qr, which is 9times the influent flow, or 9 Qi. During the typical filtrationoperation, backwash pump 51 is off, backwash valve 63 is closed and airsupply valves 83, 84 are closed.

As indicated, an important aspect of the present inventions is thedewatering, thickening and removal of the spent SPAC 12 (and itsadsorbed contaminants). When the SPAC has reached breakthrough, theinfluent flow into the system is shut off, feed pump 16 is off and SPACfeed valve 18 closed. Recycle pump 26 continues to operate and pumps theslurry at a rate of 10 Qi from sorption reactor 20. During thedewatering process, ceramic membrane filter 30 continues to removepermeate at a flow rate of 1 Qi and retentate continues to be returnedto sorption reactor 20 at a rate of 9 Qi. After a certain amount oftime, which is based upon the size (retention time) of the sorptionreactor 20, the exhausted SPAC is sufficiently dewatered andconcentrated to be removed for disposal. The desired concentration ofSPAC 12 slurry when removed is, as an example, 10 grams of carbon/liter.If the concentration is too high, it is difficult to remove from thesystem.

It should also be noted that in practice, when concentrating theretentate for removal, after the influent flow Qi to the sorptionreactor 20 is shut down, permeate is typically not removed at the fulldesired rate of 1 Q for the entire process. Instead, it is ramped downto less than 1 Q so that the retentate does not become too thick orconcentrated for effective removal from the system.

When backwashing the membranes of the ceramic membrane filter 30 isrequired, the influent flow as described above for dewatering is halted.Recycle pump 26 is off and drain valve 39 is open. Permeate valve 33 isclosed and backwash valve 63 and 66 are open. Backwash pump 61 isactivated, drawing permeate from permeate tank 50. The permeate flowsalong backwash line 62 to backwash tank 70. If desired, chemicals may beadded to the permeate along backwash line 62 via chemical feed line 65.The permeate or chemically enhanced permeate flows from backwash line 62into permeate line 32 in a reverse flow from the permeate. Thebackwashed permeate goes through the ceramic membrane filter 30 in areverse direction from filtration. The backwash liquid reverse flows toslurry effluent line 22 and is removed through open drain valve 59.

The above description is not intended to limit the meaning of the wordsused in or the scope of the following claims that define the invention.Rather, it is contemplated that future modifications in structure,function or result will exist that are not substantial changes and thatall such insubstantial changes in what is claimed are intended to becovered by the claims. Thus, while preferred embodiments of the presentinventions have been illustrated and described, it will be understoodthat changes and modifications can be made without departing from theclaimed invention. In addition, although the term “claimed invention” or“present invention” is sometimes used herein in the singular, it will beunderstood that there are a plurality of inventions as described andclaimed.

Various features of the present inventions are set forth in thefollowing claims.

1. A method for removing contaminants from water comprising the stepsof: 1) adding 0.5 to 2.0 grams of carbon/liter (i.e. 500 to 2,000 mg ofcarbon/liter) of sub-micron powdered activated carbon (SPAC) to aninfluent flow of water to be treated; 2) combining the SPAC with thewater to be treated, equating to 500 to 2,000 mg of carbon/liter of avolume of a pressurized sorption reactor; 3) introducing a SPAC andwater mixture into the pressurized sorption reactor for treatment, thepressurized sorption reactor having a horizontal baffle; 4) permittingthe mixture to remain in the pressurized sorption reactor for a maximum30 to 60 minute retention time for the SPAC to adsorb contaminants inthe water; and 5) transferring the mixture from the pressurized sorptionreactor using a recycle pump to a high velocity ceramic membrane filterunit operating in cross-flow filtration wherein the treated water isdischarged as permeate and the SPAC is returned to the pressurizedsorption reactor as retentate.
 2. The method of claim 1, including thesteps of: 1) removing the SPAC and adsorbed contaminant concentrate fromthe ceramic membrane filter via a concentrate line upon the SPACreaching breakthrough; and 2) adding new SPAC to the influent flow ofwater to continue contaminant removal.
 3. The method of claim 1 whereinthe influent flow is 1 Q and the mixture of SPAC and influent is pumpedat 10 times the influent (10 Q) from the pressurized sorption reactor tothe ceramic membrane filter.
 4. The method of claim 3 wherein thepermeate is discharged at a rate of 1 times the influent flow from theceramic membrane filter and the retentate is returned to the pressurizedsorption reactor at a rate of 9 times the influent flow (9 Q).
 5. Themethod of claim 4 wherein the SPAC has a mean particle diameter belowapproximately 1 micron.
 6. The method of claim 2 wherein the SPAC andadsorbed contaminants are thickened for removal by terminating theinfluent flow to the pressurized sorption reactor and continuingoperation of the recycle pump until the retentate is thickened and isthereafter removed via the concentrate line for disposal.
 7. The methodof claim 5 wherein the ceramic membrane filter has a nominal pore sizebarrier of approximately 0.1 microns. 8.-12. (canceled)